In general, a memory device comprises a nonvolatile memory, and a memory controller comprising a volatile memory. The nonvolatile memory is an electrically erasable and rewritable nonvolatile memory, that is, an Electrically Erasable Programmable Read-Only Memory (EEPROM), for example, a NAND flash memory. The volatile memory is, for example, a Static RAM (SRAM) or a Dynamic RAM (DRAM). The nonvolatile memory reads or writes data page by page and erases data block by block. Thus, the nonvolatile memory requires a long time to randomly access the storage area in comparison with the volatile memory. Therefore, the memory device uses the volatile memory provided in the memory controller as a cache memory. The memory device stores system data including conversion tables between logical addresses and physical addresses (hereinafter, simply referred to as conversion tables) in the system area of the nonvolatile memory. When the power is turned on, the memory device reads part of system data from the nonvolatile memory, and stores the read data in the volatile memory provided in the memory controller. The memory controller converts a logical address accessed from a host into a physical address with reference to the conversion tables of the volatile memory. When a conversion table corresponding to the logical address accessed from the host is not stored in the volatile memory, the memory controller newly reads a conversion table from the nonvolatile memory, and updates and manages the conversion tables of the volatile memory. Thus, when the conversion tables of the volatile memory are updated at each random access from the host, the access performance of the storage device is degraded.